The purpose of the LIFE Study is to assess the impact of environmental factors, broadly defined to include lifestyle factors, on human reproduction and development. The LIFE Study is consistent with the mission of the National Institute of Child Health and Human Development that includes conducting basic, clinical and epidemiologic research focusing on factors and processes associated with human reproduction and development thereby, ensuring the birth of healthy infants capable of reaching full adult potential unimpaired by physical or mental disabilities. This study will assess the relation between select environmental factors and human fecundity and fertility. This research proposes to recruit and retain 800 couples interested in becoming pregnant and willing to participate in a longitudinal study. Couples will be selected from geographic regions that were chosen from peer reviewed competitive proposals. Fecundity will be measured by the time required for the couples to achieve pregnancy, while fertility will be measured by the ability of couples to have a live born infant. Infertility will be recognized for couples unable to conceive within 12 months of trying. The studys primary environmental exposures include: organochlorine pesticides; polychlorinated biphenyls; polybrominated diphenyl ethers; metals; perfluorinated compounds; cotinine; and phytoestrogens. A growing body of literature suggests these compounds may exert adverse effects on human reproduction and development; however, definitive data are lacking especially for sensitive endpoints. Couples will participate in a 25-minute baseline interview and be instructed in the use of home fertility monitors and pregnancy kits for counting the time required for pregnancy and detecting pregnancy. Blood and urine samples will be collected at baseline from both partners of the couple for measurement of the environmental exposures. Two semen samples from male partners and two saliva samples from female partners also will be requested. Semen samples will be used to globally assess male fecundity as measured primarily by sperm concentration and morphology. Saliva samples will be used for the measurement of cortisol levels as a marker of stress among female partners so that the relation between environmental factors, stress and human reproduction can be assessed. Data analysis is underway with a number of environmental chemicals associated with diminished couple fecundity.